Mark IIC+ Schematic (correct!)

[jrb32]

Hi Guys,

I was so annoyed with all the misinformation out there that I've drawn up an accurate IIC+ schematic of the main sections. This includes information I can find regarding the ++ mods. This is taken from info I can find on here from chipaudette who had an RP10A IIC converted to a IIC+ by Mike B and all the great IIC+ info from Boogiebabies that's on here. Thanks so much for this info! I also bought an RP10A IIC later which was then upgraded to a IIC+ and can confirm everything is accurate as possible and traced for the RP10A. I've also seen enough photos of other IIC+s (RP11A, SP11A) to know that they all end up the same circuit wise.

Anyway the schematic is here. Hope it's of use to someone!

IIC+ Schematic: https://drive.google.com/open?id=1ieTnMLeSiNDoXu_9Or0ky2RIDwbLAcUQ

Enjoy!

 

[jediguitarist]

Wow. Great work! I wish I even remotely knew what any of that means. Hahha.

Would be awesome to be able to troubleshoot my amps instead of just changing tubes and hoping that fixes the problem. :lol:

 

[tony777]

Awesome!!!!

 

[modder]

This was really useful for me for comparing my Mark III for the + mod!

The 100k resistor after the volume you've labelled as optional, is that for the ++ mod? It's not on the other schematics I've seen or anything for the Mark IIIs.

 

[jrb32]

The 100k resistor after the volume you've labelled as optional, is that for the ++ mod? It's not on the other schematics I've seen or anything for the Mark IIIs.

It's a remnant of upgrading a IIC to a IIC+ that Mike B leaves in when upgrading a non factory IIC to a IIC+. Info I got was from here: http://forum.grailtone.com/viewtopic.php?f=27&t=40649&start=0

This 'fire breathing dragon' thing is not a ++ mod or something offered by the factory. However, it adds in even more gain when combined with a ++ mod. A simple switchable gain boost is to add the 100k resistor between the pots and then make the 15uF off V2B switchable via a push/pull middle pot and/or via a simple footswitch. Anything more than that and you've got to add in a relay.

 

[jrb32]

Link updated to include info on the ++ Mod. There seem to be two versions so have included both. One involves a component addition and the other includes adding a relay to switch similar to the Mark III.

https://drive.google.com/open?id=1ieTnMLeSiNDoXu_9Or0ky2RIDwbLAcUQ (same as link above - updated that as well)

 

[jrb32]

100% confirmed with an RP10 IIC that was upgraded to a IIC+. Links updated to correct version.

Enjoy!

 

[woodbutcher65]

Cool stuff, thanks for doing it.

Now...as I understand it, a IIC+ can have either the RP10 or RP11 preamp board in it.

Are the differences between these two preamp board understood? And how will the difference affect tone?

 

[jrb32]

Now...as I understand it, a IIC+ can have either the RP10 or RP11 preamp board in it.

Or the SP10A or SP11A for Non Reverb (RP boards - the R stands for Reverb). Read the IIC+ guide for dummies on here...

I haven't done a layout for the RP11A board or the SP10A or SP11A board. Since no two IIC+s sound the same you'll be hard pushed to understand the differences tone wise. From a circuit point of view the only difference I can tell is that C9 and R105 are swapped over in the RP11A and SP11A board so that C9 comes first off V2B. Apart from that, identical circuit wise. Layout slightly different.

The RP11A and SP11A boards were designed for the later IIC. This IIC appears to have a few features from the IIC+ (e.g. quick glance a 10M resistor for the treble shift). It was designed in mind to make it an easier upgrade to a C+.

From the guide for dummies:

The RP-10A is based in the style of the IIB with LDR's for switching instead of the one relay. The RP-11A is the circuit board that was
redesigned for the IIC with a much different layout. It was also later the board used in the IIC+ with many component changes and
a different circuit layout. From what I could find out about the RP-10A, it was the early production IIC PCB. It was changed somewhere in the mid range
to the RP-11 in mid to late 1983. Hence, both boards have 1983 copyrights.

I should probably have a look at the IIB schematic - trace that out and go from there to check differences/similarities with the IIC RP10A when I get some time. I think they're completely different circuit designs though but could be wrong.

Perhaps the RP10A board features in some of the late IIBs? The LDRs were designed to stop popping when switching between channels. Either way once the + mod is done to them on all the boards, they end up the same circuit wise. It's just a lot harder to do on the RP10 and SP10 I would think.

For differences between the two... two identical IIC+s with the same board and the same month of production will sound completely different so good luck!

 

[discostu29]

I have recently bought a IIC++ modded in 2016 by Mike B just wondering if you would be interested in photos etc to figure out the mods done from + to ++?

Mike B may retire anytime now and will take the mod with him, i think there will be interest in this mod.

 

[Dan__O]

I've updated the SLOCLONES version (finally). Should be 99% correct.
Check out the JB version for and impressive amount of extra info on mods etc. This is just what we worked out from trawling gutshots for months. A rebuild of a MK2B which I converted to MK2C+ forced me to fix the schematic.

http://sites.google.com/site/danoampstuff/mesa/Mesa_MK2C+_SLOCLONE_v2.pdf

 

[Amimaster]

Hello Jrb32!
Thanks for your work, it seems to me the most clear schematics around.
I'm no expert of tube amps, actually I'm using your schematics along with Merlin's book to study the subject and try to build my first amp. However, I think that V5B should be upside-down, as it is it seems like in a sort of cascode configuration. Also Red/Blue wire should be 60V, am I right?

 

[Matador]

I've updated the SLOCLONES version (finally). Should be 99% correct.
Check out the JB version for and impressive amount of extra info on mods etc. This is just what we worked out from trawling gutshots for months. A rebuild of a MK2B which I converted to MK2C+ forced me to fix the schematic.

http://sites.google.com/site/danoampstuff/mesa/Mesa_MK2C+_SLOCLONE_v2.pdf

That schematic has a strange connection for the bottom two tone pots (bass and middle), which is different from the JB schematic earlier (and the original Mesa one).

Can anyone confirm the SLOClone schematic arrangement is correct?

 

[domglop78]

hello
Very good informations for all people who love mark serie's.

To add more informations and because this kind of amplification are very old now, it seem's very important to propose a PCB circuit. (impossible to find and repare this old amp around in the world)
The pcb circuit will build manualy like the old process. we just need a master calque with all the jonctions and the implantation of the composants.

this is the occasion to realize a new life for all mark 2 amps.

Why not to engage the same idea for Mark1 ,3,4 or 5 ?

When i was young i realize some PCB for many electronic system.... (tv , audio, cars....) with the old pcb process ( Realization on tracing calque, UV process and engraving with revelation of PCB)

To continue playing with Mesa amp it is very important to look this process and showing for all the best sound for bass and guitar player.

To ear you about this idea next time
best regards
dom

 

[Boogiebabies]

The problem is that the RP11A is not patented, it’s
Got a copyright on the PCB. Therefore, you can probably make
One, but not sell them in the US.

 

[jrb32]

Hello Jrb32!
Thanks for your work, it seems to me the most clear schematics around.
I'm no expert of tube amps, actually I'm using your schematics along with Merlin's book to study the subject and try to build my first amp. However, I think that V5B should be upside-down, as it is it seems like in a sort of cascode configuration. Also Red/Blue wire should be 60V, am I right?

Hey sorry for the slow reply. That makes sense I'm going off the original schematic here which deliberately contained errors so you're probably correct! Good spot

 

[jrb32]

The problem is that the RP11A is not patented, it’s
Got a copyright on the PCB. Therefore, you can probably make
One, but not sell them in the US.

I think copyright only lasts for 10 years on PCB design in the USA. I think the harder thing would be mass producing a double sided etched PCB to the same standards as done up to the Mk IIC. As far as I am aware since technology has moved on, nobody produces PCBs this way anymore. For a MKIII onwards these use modern PCB manufacturing.

I have thought about making some Mesa PCBs for the older amps (prior to the MkIII) but firstly they're basically bullet proof and even if snapped in half can be repaired easily. Secondly, it's opens the Pandora's box to a lot of hobbyists screwing around with old mesa amps which need to be left alone and preserved trying to do a IIB to IIC+ upgrade themselves or a III to IIC+ or whatever

 

[Henz]

That schematic has a strange connection for the bottom two tone pots (bass and middle), which is different from the JB schematic earlier (and the original Mesa one).

Can anyone confirm the SLOClone schematic arrangement is correct?

Greetings. I just briefed it. The tone stack appears to be the same as Jrb32's. Blessings.

 

[Henz]

I think copyright only lasts for 10 years on PCB design in the USA. I think the harder thing would be mass producing a double sided etched PCB to the same standards as done up to the Mk IIC. As far as I am aware since technology has moved on, nobody produces PCBs this way anymore. For a MKIII onwards these use modern PCB manufacturing.

I have thought about making some Mesa PCBs for the older amps (prior to the MkIII) but firstly they're basically bullet proof and even if snapped in half can be repaired easily. Secondly, it's opens the Pandora's box to a lot of hobbyists screwing around with old mesa amps which need to be left alone and preserved trying to do a IIB to IIC+ upgrade themselves or a III to IIC+ or whatever

Greetings Jon! Hey , there are two updated C+ schematics out there. One has the ++ mods shown with optional component values in some spots and the other one doesnt . though they seem both correct, which is the most recent one? Tia, Jim

 

[BigW72]

I've updated the SLOCLONES version (finally). Should be 99% correct.
Check out the JB version for and impressive amount of extra info on mods etc. This is just what we worked out from trawling gutshots for months. A rebuild of a MK2B which I converted to MK2C+ forced me to fix the schematic.

http://sites.google.com/site/danoampstuff/mesa/Mesa_MK2C+_SLOCLONE_v2.pdf

Dan_O (or anyone else)....I built a Mark IIC+ preamp based on the SloClone schematic and struggling with the EQ circuit. The power section is a basic Marshall 100W. The Amps works without the EQ by jumpering the preamp in the PI input. When I try the EQ board, I get what sounds like 60 cycle hum. I've re-done this multiple times....cleaned up my grounding and I keep getting the same result. At one point it did work with a different layout, but it was incredibly messy and I've not been able to get this back working.
Any help / input would be greatly appreciated.